1. Field of the Invention
This invention relates a telephone exchange apparatus which accommodates a plurality of outside lines and a plurality of extension terminals and converts the levels of signals received from the outside lines.
2. Description of the Prior Art
In a case where an extension accommodates an individual telephone (an analog telephone) in a conventional telephone exchange apparatus, the level in the telephone exchange is adjusted so as to assure equal speech quality even if the individual telephone is connected to the extension or even if it is directly connected to a main wire.
Further, in a case where a leased telephone of a telephone exchange apparatus is accommodated in an extension in the conventional telephone exchange apparatus, the arrangement is such that by adjusting the overall gain of the leased telephone and the telephone exchange apparatus, the optimum speech quality is obtained when the leased telephone carries on a telephone conversion by an analog line.
Owing to the greater popularity of digital communication networks, situations in which the main wire of a telephone exchange apparatus accommodates a digital line are increasing.
With regard to a telephone conversation via a digital line in the conventional telephone exchange apparatus, the gain within the apparatus is set at 0 dB in order to assure a speech quality equal to that which prevails when a digital telephone connected to an extension is connected to a digital network. In other words, the conventional telephone exchange apparatus is so adapted that data identical with the incoming data from an outside line is transmitted to the extension telephone.
However, when a signal from a digital network is received in an individual telephone accommodated in the conventional telephone exchange apparatus, a problem which arises is that the sound volume of the received speech is too large. Furthermore, even in the case of a leased telephone accommodated in the conventional telephone exchange apparatus, the gain is adjusted so as to obtain the optimum speech quality if the telephone conversation is carried on by an analog line, as mentioned above. When a signal is received from a digital network, however, the sound volume of the received speech is too large.